Risk assessment of pesticides used in the eastern Avocado Belt of Michoacan, Mexico: A survey and water monitoring approach.

Pesticides use raises concerns regarding environmental sustainability, as pesticides are closely linked to the decline of biodiversity and adverse human health outcomes. This study proposed a holistic approach for assessing the potential risks posed by pesticides for human health and the environment in the eastern region of Michoacan, where extensive agricultural lands, especially corn and avocado fields, surround the Monarch Butterfly Biosphere Reserve. We used a combination of qualitative (semi-structured interviews) and quantitative (chemical analysis) data. Fifty-five interviews with smallholder farmers allowed us to identify pesticide types, quantities, frequencies, and application methods. A robust and precise analytical method based on solid-phase extraction and LC-MS/MS was developed and validated to quantify 21 different pesticides in 16 water samples (rivers, wells, runoff areas). We assessed environmental and human health risks based on the pesticides detected in the water samples and reported in the interviews. The interviews revealed the use of 28 active ingredients, including glyphosate (29 % of respondents), imidacloprid (27 %), and benomyl (24 %). The pesticide analysis showed the presence of 13 different pesticides and degradation products in the water samples. The highest concentrations were found for imidacloprid (1195 ngL-1) and carbendazim (a degradation product of benomyl; 932 ngL-1), along with the metabolite of pyrethroid insecticides, 3-PBA (494 ngL-1). The risk assessment indicates that among the most used pesticides, the fungicide benomyl and carbendazim pose the highest risk to human health and aquatic ecosystems, respectively. This study unveils novel insights on agricultural practices for the avocado, a globally consumed crop that is undergoing rapid production expansion. It calls for the harmonisation of crop protection with environmental responsibility, safeguarding the health of the people involved and the surrounding ecosystems.

Faster and more precise isotopic water analysis of discrete samples by predicting the repetitions' asymptote instead of averaging last values.

Water stable isotope analysis using Cavity Ring-Down Spectroscopy (CRDS) has a strong between-sample memory effect. The classic approach to correct this memory effect is to inject the sample at least 6 times and ignore the first two to three injections. The average of the remaining injections is then used as measured value. This is in many cases insufficient to completely compensate the memory effect. We propose a simple approach to correct this memory effect by predicting the asymptote of consecutive repeated injections instead of averaging over them. The asymptote is predicted by fitting a y = a x + b relation to the sample repetitions and keeping b as measured value. This allows to save analysis time by doing less injections while gaining precision. We provide a Python program applying this method and describe the steps necessary to implement this method in any other programming language. We also show validation data comparing this method to the classical method of averaging over the last couple of injections. The validation suggests a gain in time of a factor two while gaining in precision at the same time. The method does not have any specific requirements for the order of analysis and can therefore also be applied to an existing set of analyzes in retrospect.•We fit a simple y = a x + b relation to the sample repetitions of Picarro L2130-i isotopic water analyzer, in order to keep the asymptote (b) as measured value instead of using the average over the last couple of measurements.•This allows a higher precision in the measured value with less repetitions of the injection saving precious time during analysis.•We provide a sample code using Python, but generally this method is easy to implement in any automated data treatment protocol.

Spatial dependency of arsenic, antimony, boron and other trace elements in the shallow groundwater systems of the Lower Katari Basin, Bolivian Altiplano.

Spatial patterns, cluster or dispersion trends are statistically different from random patterns of trace elements (TEs), which are essential to recognize, e.g., how they are distributed and change their behavior in different environmental processes and/or in the polluted/contaminated areas caused by urban and industrial pollutant located in upstream basins and/or by different natural geological conditions. The present study focused on a statistical approach to obtain the spatial variability of TEs (As, B and Sb) in shallow groundwater (GW) in a high-altitude arid region (Lower Katari Basin, Bolivian Altiplano), using multivariate analysis (PCA and HCA), geochemical modeling (PHREEQC, MINTEQ) and spatial analyses (Moran's I and LISA), considering the community supply wells. The results indicate that despite of the outliers there is a good autocorrelation in all cases, since Moran's I values are positive. The global spatial dependence analysis indicated a positive and statistically significant spatial autocorrelation (SA) for all cases and TEs are not randomly distributed at 99% confidence level. The results of hydrochemical modeling suggested the precipitation and stability of Fe (III) phases such as goethite. The re-adsorption of As and Sb on the mineral surface in the aquifer could be limiting the concentrations of both metalloids in southern regions. Spatial autocorrelation was positive (High-High) in northwestern (arsenic), southeastern (boron) and northeastern (antimony) region. The results reflected that the As and Sb are the main pollutants linked to the natural geological conditions, but B is a main pollutant due to the anthropogenic activities. Furthermore, >50% shallow groundwater exceeded the WHO limit and NB-512 guideline values for Sb (87%), B (56%) and As (50%); therefore the spatial distribution and concentrations of these TEs in GW raise a significant concern about drinking water quality in the study area.

Extreme Arsenic Bioaccumulation Factor Variability in Lake Titicaca, Bolivia.

Latin America, like other areas in the world, is faced with the problem of high arsenic (As) background in surface and groundwater, with impacts on human health. We studied As biogeochemical cycling by periphyton in Lake Titicaca and the mine-impacted Lake Uru Uru. As concentration was measured in water, sediment, totora plants (Schoenoplectus californicus) and periphyton growing on stems, and As speciation was determined by X-ray absorption spectroscopy in bulk and EDTA-extracted periphyton. Dissolved arsenic was between 5.0 and 15 µg L-1 in Lake Titicaca and reached 78.5 µg L-1 in Lake Uru Uru. As accumulation in periphyton was highly variable. We report the highest As bioaccumulation factors ever measured (BAFsperiphyton up to 245,000) in one zone of Lake Titicaca, with As present as As(V) and monomethyl-As (MMA(V)). Non-accumulating periphyton found in the other sites presented BAFsperiphyton between 1281 and 11,962, with As present as As(III), As(V) and arsenosugars. DNA analysis evidenced several taxa possibly related to this phenomenon. Further screening of bacterial and algal isolates would be necessary to identify the organism(s) responsible for As hyperaccumulation. Impacts on the ecosystem and human health appear limited, but such organisms or consortia would be of great interest for the treatment of As contaminated water.

4-nitroso-sulfamethoxazole generation in soil under denitrifying conditions: Field observations versus laboratory results.

The formation of 4-nitroso-sulfamethoxazole and 4-nitro-SMX, two transformation products (TPs) of sulfamethoxazole (SMX) was investigated under batch soil slurry experiments and in a field study. Due to their low occurrence levels (ng/L) in environmental waters, a suitable analytical method based on liquid chromatography - high resolution - mass spectrometry was developed. Consequently, field observations revealed, for the first time, the occurrence of 4-nitroso-SMX in groundwater at concentrations as high as 18ng/L.Nitric oxide (NO) steady-state concentrations were determined in soil slurry experiments because this reactive specie accounted for the formation of 4-nitroso-SMX and 4-nitro-SMX. Measurements revealed that environmental SMX concentrations (0.2-2µg/L) at neutral pH induced the accumulation of nitric oxide. Under acidic conditions (pH<6), nitrous acid (HONO) was the major source of nitric oxide while under neutral/basic conditions nitric oxide release was related to the inhibition of denitrification processes. Under laboratory experiments, SMX nitration reaction appeared to be an irreversible transformation pathway, while 4-nitroso-SMX was slowly transformed over time. The occurrence of 4-nitroso-SMX conditions was therefore unexpected in the field study but could be due to its continuous input from soil and/or its relative persistence under anoxic conditions. A mechanism for 4-nitroso-SMX formation was proposed involving a nitrosative desamination pathway through a phenyl radical.

Biotic nitrosation of diclofenac in a soil aquifer system (Katari watershed, Bolivia).

Up till now, the diclofenac (DCF) transformation into its nitrogen-derivatives, N-nitroso-DCF (NO-DCF) and 5-nitro-DCF (NO2-DCF), has been mainly investigated in wastewater treatment plant under nitrification or denitrification processes. This work reports, for the first time, an additional DCF microbial mediated nitrosation pathway of DCF in soil under strictly anoxic conditions probably involving codenitrification processes and fungal activities. This transformation pathway was investigated by using field observations data at a soil aquifer system (Katari watershed, Bolivia) and by carrying out soil slurry batch experiments. It was also observed for diphenylamine (DPA). Field measurements revealed the occurrence of NO-DCF, NO2-DCF and NO-DPA in groundwater samples at concentration levels in the 6-68s/L range. These concentration levels are more significant than those previously reported in wastewater treatment plant effluents taking into account dilution processes in soil. Interestingly, the p-benzoquinone imine of 5-OH-DCF was also found to be rather stable in surface water. In laboratory batch experiments under strictly anoxic conditions, the transformation of DCF and DPA into their corresponding N-nitroso derivatives was well correlated to denitrification processes. It was also observed that NO-DCF evolved into NO2-DCF while NO-DPA was stable. In vitro experiments showed that the Fisher-Hepp rearrangement could not account for NO2-DCF formation. One possible mechanism might be that NO-DCF underwent spontaneous NO loss to give the resulting intermediates diphenylaminyl radical or nitrenium cation which might evolve into NO2-DCF in presence of NO2 radical or nitrite ion, respectively.

Transporte de Atrazina en un Andosol y un Vertisol de México / Atrazine Transport in a Mexican Andosol and Vertisol / Transporte de Atrazina em um Andosol e um Vertisol de México

El problema de migración de plaguicidas en los campos agrícolas se estudia tradicionalmente a través del muestreo periódico de suelos, aguas y cultivos. Existen métodos más avanzados que permiten reducir el costo de los análisis en campo y pronosticar el riesgo de contaminación del medio ambiente. Estos métodos están basados en la simulación matemática del movimiento de plaguicidas. Se estudió el proceso de migración de atrazina en un suelo volcánico Andosol y un Vertisol de México en experimentos de laboratorio en columnas empacadas. En los experimentos se aplicaron diferentes dosis de atrazina y se estableció un flujo insaturado de agua bajo régimen permanente. Se utilizaron los marcadores del agua 18O y Br- para comparar los procesos de movimiento del agua y la atrazina. Se midieron los componentes del balance de masa de atrazina y agua, y su dinámica de elusión. Se aplicó la teoría del movimiento de sustancias químicas para interpretar los resultados experimentales y obtener las propiedades principales de transporte de atrazina en ambos suelos. Los resultados señalan que la atrazina se mueve en el Andosol 10-16 veces más lentamente que el agua y en el Vertisol el movimiento es 2,5 veces más lento. Se determinaron valores de cinco propiedades de transporte de atrazina que permiten predecir la migración del plaguicida, minimizar el muestreo en el campo y estimar el riesgo de contaminación del suelo y del acuífero aplicando los métodos de cálculo existentes en la literatura.

The problem of pesticide migration in agricultural lands is traditionally studied by means of periodical soil, water and plant sampling. More advanced methods are available today, which permit to reduce the costs of field analysis and to predict environmental contamination risk. These methods are based on mathematical simulation of pesticide movement. The process of atrazine migration in a volcanic soil Andosol and a Vertisol of Mexico was studied by means of laboratory experiments in packed columns. Different atrazine doses and steady state unsaturated water flow were applied in the experiments. The 18O and Br- water tracers were used to compare atrazine and water movement. The atrazine and water mass balance components were measured, as well as the dynamics of elution. The chemical substances movement theory was applied to interpret the experimental results and to obtain the principal properties of atrazine transport in both soils. The results show that atrazine moves in the Andosol 10-16 times slower than water, and 2.5 times slower in the Vertisol. Five properties of atrazine transport were determined, which can be used to predict the migration of this pesticide so as to minimize the sampling effort in the field, and to assess the risk of soil and aquifer contamination by calculation methods reported in the literature.

O problema de migração de praguicidas em áreas agrícolas se estuda tradicionalmente através da amostragem periódica de solos, aguas e cultivos. Existem métodos mais avançados que permitem reducir o custo das análises em campo e prever o risco de contaminação do meio ambiente. Estes métodos estão baseados em simulação matemática do movimento de praguicidas. Estudou-se o processo de migração de atrazina em um solo vulcánico Andosol e um Vertisol do México em experimentos de laboratório em colunas empacotadas. Nos experimentos se aplicaram diferentes doses de atrazina e se estabeleceu um fluxo insaturado de água sob regime permanente. Utilizaram-se os marcadores da água 18O e Br‾ para comparar os processos de movimento da água e a atrazina. Mediram-se os componentes do balanço de massa de atrazina e água, e sua dinâmica de eluição. Aplicou-se a teoria do movimento de substâncias químicas para interpretar os resultados experimentais e obter as propiedades principais de transporte de atrazina em ambos os solos. Os resultados indicam que a atrazina se movimenta no Andosol 10-16 veces mais lentamente que a água e no Vertisol o movimento é 2,5 vezes mais lento. Determinaram-se valores de cinco propriedades de transporte de atrazina que permitem predizer a migração do praguicida, minimizar a amostragem no campo e estimar o risco de contaminação do solo e do aquífero aplicando os métodos de cálculo existentes na literatura.

Biodegradation of petroleum hydrocarbon vapors: laboratory studies on rates and kinetics in unsaturated alluvial sand.

Predictions of natural attenuation of volatile organic compounds (VOCs) in the unsaturated zone rely critically on information about microbial biodegradation kinetics. This study aims at determining kinetic rate laws for the aerobic biodegradation of a mixture of 12 volatile petroleum hydrocarbons and methyl tert-butyl ether (MTBE) in unsaturated alluvial sand. Laboratory column and batch experiments were performed at room temperature under aerobic conditions, and a reactive transport model for VOC vapors in soil gas coupled to Monod-type degradation kinetics was used for data interpretation. In the column experiment, an acclimatization of 23 days took place before steady-state diffusive vapor transport through the horizontal column was achieved. Monod kinetic parameters Ks and vmax could be derived from the concentration profiles of toluene, m-xylene, n-octane, and n-hexane, because substrate saturation was approached with these compounds under the experimental conditions. The removal of cyclic alkanes, isooctane, and 1,2,4-trimethylbenzene followed first-order kinetics over the whole concentration range applied. MTBE, n-pentane, and chlorofluorocarbons (CFCs) were not visibly degraded. Batch experiments suggested first-order disappearance rate laws for all VOCs except n-octane, which decreased following zero-order kinetics in live batch experiments. For many compounds including MTBE, disappearance rates in abiotic batch experiments were as high as in live batches indicating sorption. It was concluded that the column approach is preferable for determining biodegradation rate parameters to be used in risk assessment models.

Uptake of arsenic by New Zealand watercress (Lepidium sativum).

Watercress (Lepidium sativum) is consumed as a vegetable, especially by the indigenous community in New Zealand. An investigation was carried out on the accumulation of arsenic by watercress, following earlier reports of inordinate arsenic concentrations in some aquatic macrophytes collected from the Waikato River, North Island, New Zealand. The Waikato River and some other aquatic systems in Taupo Volcanic Zone, New Zealand have elevated arsenic concentrations due to geothermal activity. Watercress, river water and sediment samples were collected from 27 sites along the Waikato river and analysed for arsenic. Greenhouse trials with watercress grown in beakers containing added arsenic were conducted to confirm the ability of this species to accumulate arsenic. At a number of sites, the concentration of arsenic in both the water and the watercress samples exceeded the World Health Organisation (WHO) limit for drinking water (0.01 mg l(-1)) and foodstuffs (2 mg kg(-1) on a fresh weight basis). The average leaf and stem arsenic concentrations were, respectively, 29.0 and 15.9 mg kg(-1) on a fresh weight basis. Plants grown in solutions of >0.4 mg l(-1) arsenic concentration had fresh weight arsenic concentrations above the WHO limit. Despite these higher concentrations, arsenic levels in plants grown under greenhouse conditions were approximately fivefold lower than in plants growing in the Waikato River, possibly because under natural conditions, the watercress is rooted in sediment containing on average approximately 35 mg kg(-1) arsenic. It is recommended that watercress from the Waikato River, or other areas with elevated water arsenic concentrations, should not be consumed.